System and method for I/Q imbalance compensation

Abstract

A transmitter ( 102 ) generates a first set of data symbols and a first pilot symbol ( 601 ) at a first time, and a second set of data symbols and a second pilot symbol ( 602 ) at a different, second time. The first ( 601 ) and second ( 602 ) pilot. symbols are each represented by first ( 701 ) and second ( 702 ) pilot carriers, respectively, located at first ( 703 ) and second ( 704 ) predetermined sample frequencies, respectively, in a channel bandwidth. For the first pilot symbol ( 601 ), the first ( 701 ) and second ( 702 ) pilot carriers have first and second predetermined values, respectively. For the second pilot symbol ( 602 ), the first ( 701 ) and second ( 702 ) pilot carriers have third and fourth predetermined values, respectively. A receiver ( 104 ) measures the first, second, fourth and third predetermined values responsive to receiving the first ( 601 ) and second ( 602 ) pilot symbols to determine first, second, third and fourth estimates of channel distortion, respectively, for compensating and recovering the first and the second sets of data symbols.

1. A method of transmitting comprising:
 generating a first transmit signal with a signal generator, the first transmit signal including a first plurality of data symbols and a first pilot symbol, at a first transmit time, wherein the first pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel; and 
 generating a second transmit signal with the signal generator, the second transmit signal including a second plurality of data symbols and a second pilot symbol, at a different, second transmit time, wherein the second pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, which is different than the third predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel. 
 
     
     
       2. The method of transmitting according to  claim 1  further comprising:
 selecting the first and third predetermined sample frequencies to be sufficiently close such that channel conditions are similar for both the first and third predetermined sample frequencies; and 
 selecting the second and fourth predetermined sample frequencies to be sufficiently close such that channel conditions are similar for both the second and fourth predetermined sample frequencies. 
 
     
     
       3. The method of transmitting according to  claim 1  further comprising:
 selecting the first and second pilot carriers to be symmetrically located about a direct current (DC) frequency in the bandwidth of the communication channel; and 
 selecting the third and fourth pilot carriers to be symmetrically located about the DC frequency in the bandwidth of the communication channel. 
 
     
     
       4. The method of transmitting according to  claim 1  further comprising:
 with the signal generator: 
 generating the first transmit signal at the first transmit time; and 
 generating the second transmit signal at the second transmit time, wherein the first transmit time and the second transmit time are spaced apart in time. 
 
     
     
       5. The method of transmitting according to  claim 2  further comprising:
 selecting the pilot carriers of the first pilot symbol to be located at carrier locations +/−k for multiple spaced k, where k is an integer value; and 
 selecting the pilot carriers of the second pilot symbol to be located at carrier locations +/−j for multiple spaced j, where j is an integer value. 
 
     
     
       6. The method of transmitting according to  claim 1  further comprising:
 transmitting the first transmit signal on a first transmit antenna; and 
 transmitting the second transmit signal on a second transmit antenna. 
 
     
     
       7. A method of transmitting comprising:
 generating a transmit signal with a signal generator, including a first plurality of data symbols and a first pilot symbol, at a first transmit time, wherein the first pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel; and 
 the transmit signal also including a second pilot symbol, wherein the second pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, which is different than the third predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel, the first and third predetermined sample frequencies being sufficiently close such that channel conditions are similar for both the first and third predetermined sample frequencies, and second and fourth predetermined sample frequencies being sufficiently close such that channel conditions are similar for both the second and fourth predetermined sample frequencies; 
 wherein the first and second pilot carriers are symmetrically located about a direct current (DC) frequency in the bandwidth of the communication channel, and the third and fourth pilot carriers are symmetrically located about the DC frequency. 
 
     
     
       8. An apparatus comprising:
 a signal generator adapted to generate pilot symbols located in time and frequency; 
 a transmitter adapted to transmit an orthogonal frequency division multiplexing (OFDM) signal containing the pilot symbols, wherein the signal generator is adapted to: 
 generate a first transmit signal, including a first plurality of data symbols and a first pilot symbol, at a first transmit time, wherein the first pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel; and 
 generate a second transmit signal, including a second plurality of data symbols and a second pilot symbol, at a different, second transmit time, wherein the second pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, which is different than the third predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel. 
 
     
     
       9. The apparatus of  claim 8 , wherein the signal generator is adapted to select the first and third predetermined sample frequencies to be sufficiently close such that channel conditions are similar for both the first and third predetermined sample frequencies, and to select the second and fourth predetermined sample frequencies to be sufficiently close such that channel conditions are similar for both the second and fourth predetermined sample frequencies;
 wherein the first and second pilot carriers are symmetrically located about a direct current (DC) frequency in the bandwidth of the communication channel, and the third and fourth pilot carriers are symmetrically located about the DC frequency in the bandwidth of the communication channel. 
 
     
     
       10. The apparatus of  claim 8 , wherein the first transmit signal, generated at the first transmit time, and the second transmit signal, generated at the second transmit time, are spaced apart in time. 
     
     
       11. The apparatus of  claim 9  further comprising:
 a first transmit antenna for transmitting the first transmit signal and a second transmit antenna for transmitting the second transmit signal. 
 
     
     
       12. An apparatus comprising:
 a signal generator adapted to generate pilot symbols located in time and frequency; 
 a transmitter adapted to transmit an orthogonal frequency division multiplexing (OFDM) signal containing the pilot symbols, wherein the signal generator is adapted to: 
 generate a first transmit signal, including a first plurality of data symbols and a first pilot symbol, at a first transmit time, wherein the first pilot symbol is represented by a first pilot carrier, having a first predetermined value, and a second pilot carrier, having a different, second predetermined value, located at a first predetermined sample frequency and a second predetermined sample frequency, respectively, in a bandwidth of a communication channel; and 
 the transmit signal also including a second pilot symbol, wherein the second pilot symbol is represented by a third pilot carrier, having a third predetermined value, and a fourth pilot carrier, having a fourth predetermined value, which is different than the third predetermined value, located at a third predetermined sample frequency and a fourth predetermined sample frequency, respectively, in the bandwidth of the communication channel, the first and third predetermined sample frequencies being sufficiently close such that similar channel conditions exist for both the first and third predetermined sample frequencies, and the second and fourth predetermined sample frequencies being sufficiently close such similar channel conditions exist for both the second and fourth predetermined sample frequencies; 
 wherein the first and second pilot carriers are symmetrically located about a direct current (DC) frequency in the bandwidth of the communication channel, and the third and fourth pilot carriers are symmetrically located about the DC frequency in the bandwidth of the communication channel.